Q: What is the difference between my local time and the time on JTWC's
products?

A: The time referenced in all JTWC products is called Coordinated
Universal Time (UTC). The U.S. military refers to UTC time as "Zulu"
(Z) time. The use of UTC time is standard practice for most weather
organizations as recommended by the World Meteorological Organization (WMO), an
agency of the United Nations. To convert from Z to your local time, go to this site

(note: clicking
on this link will redirect your browser to a commercial website unaffiliated
with JTWC).

Q:
What do "Low", "Medium", and "High" mean on the
ABIO and ABPW messages?

A: "Low" formation potential describes a tropical disturbance
that is being monitored for development, but is unlikely to develop into a
significant tropical cyclone within the next 24 hours.

"Medium" formation potential describes a tropical disturbance that is
being monitored for development and has an elevated potential to develop, but
development of a significant tropical cyclone will likely occur beyond 24
hours.

"High" formation potential describes an area that is being monitored
for development and is either expected to develop within 24 hours or
development has already started, but warning criteria have not yet been met.
All areas designated as "High" will be accompanied by a Tropical
Cyclone Formation Alert.

A: A TCFA designates a disturbance that is likely to become the subject
of a JTWC tropical cyclone warning within the following 24 hour period. This
information is provided to the DoD and other U.S. government agencies for
operational planning.

Q: Why are some TCFA areas shaped like a circle and others like a rectangle?

A: Rectangular TCFA areas are issued when a developing cyclone's speed
and direction of motion can be predicted with relatively high confidence.
Circular TCFA areas are issued when a developing cyclone's speed and direction
of motion is relatively difficult to predict or if the developing cyclone is
nearly stationary.

A: JTWC initiates tropical cyclone warnings when one or more of the
following four criteria are met:

Estimated maximum sustained wind
speeds within a closed tropical circulation meet or exceed a designated
threshold of 25 knots in the North Pacific Ocean or 35 knots in the South
Pacific and Indian Oceans.

Maximum sustained wind speeds
within a closed tropical circulation are expected to increase to 35 knots
or greater within 48 hours.

A: North Pacific and North Indian Ocean tropical cyclone warnings are
routinely updated every six hours. South Indian and South Pacific
Ocean tropical cyclone warnings are routinely updated every twelve hours,
although the frequency of tropical cyclone warning issuance in these areas can
be increased to six-hourly when deemed necessary by JTWC. The REMARKS section
of each warning bulletin lists the times when the next warnings are scheduled.
When JTWC issues the final warning for a tropical cyclone, no additional
warnings are issued unless the cyclone regenerates.

A: For tropical cyclones occurring in the western Pacific and Indian
Oceans, JTWC products are transmitted no later than 3 hours past the synoptic
hour. Because the synoptic hours are 00Z, 06Z, 12Z, and 18Z, warnings will be
available by 03Z, 09Z, 15Z, or 21Z. For the eastern North Pacific Ocean, JTWC
products are transmitted no later than 4 hours after the synoptic hour (04Z,
10Z, 16Z, or 22Z).

Q: What is the shaded area around the forecast track on your warning
graphic?

A: The shaded area around the forecast track is called the "area of gale force winds." This area does not denote forecast track uncertainty. It is calculated by adding the JTWC 5-year running mean forecast track error to the forecast 34 knot wind radii at each forecast time. Since JTWC does not forecast wind radii for the 96- and 120-hour forecast times, the area of gale force winds is calculated by adding the 72-hour 34 knot radii to the forecast track error at those times. Thus, the shading highlights the area that may be affected by wind speeds exceeding 34 knots for a given JTWC forecast, based on historical track forecast errors.

Q: Why are prognostic reasoning messages only available for the western
North Pacific?

A: Per JTWC directive, prognostic reasoning messages are only required
for the western North Pacific, where there are increased U.S. Government asset
concerns. Detailed tropical cyclone analysis and forecast discussions are
included in the remarks section of warning text messages for tropical cyclones
that occur in the Indian Ocean and South Pacific Ocean.

A: JTWC issues an amended warning whenever a significant change is made
to the forecast track, intensity, and/or tropical cyclone best track position
before the next regular warning is issued. The reason for the amendment is
stated in the REMARKS section of the amended warning.

A: JTWC issues a relocated warning to indicate a significant
re-assessment of the tropical cyclone's location and movement. The term
"relocated" is used when a vector drawn from the previous warning
position to the current warning position does not reasonably represent the
actual cyclone's movement.

A: There is no "average" tropical cyclone. Tropical cyclones
are measured radially from the center to the outermost closed isobar. This
distance, in degrees latitude, determines the system's relative size (see table
below):

A: JTWC uses several tools and techniques to estimate tropical cyclone
intensity, including subjective Dvorak estimates, objective fix data, and
observations. Over most of the JTWC AOR, the Dvorak technique is the primary
means to estimate tropical cyclone intensity. The Dvorak technique is based on
the analysis of cloud patterns in visible and infrared imagery from
geostationary and polar-orbiting satellites. The Dvorak technique results in a
decimal number, called a T-number, which in turn corresponds to an intensity
estimate.

Q: What are the description labels used with tropical cyclones by JTWC?

A: In the North Pacific Ocean, a tropical cyclone with an estimated
intensity of less than 34 knots is designated a "Tropical Depression"
and a tropical cyclone with an estimated intensity between 34 and 63 knots is
designated a "Tropical Storm." Within the eastern and central North
Pacific, a tropical cyclone with an estimate intensity of 64 knots or greater
is called a "Hurricane." Within the western North Pacific, however, a
tropical cyclone with an estimated intensity between 64 and 129 knots is called
a "Typhoon," while a tropical cyclone of 130 knots or greater is
designated a "Super Typhoon." In the Indian Ocean and South Pacific,
JTWC labels ALL tropical cyclones as "Tropical Cyclone," regardless
of estimated intensity.

A: JTWC does not name tropical cyclones. JTWC uses the names determined
by the World Meteorological Organization (WMO) Tropical Cyclone Program. JTWC
will add the tropical cyclone name in parentheses after the JTWC-designated
tropical cyclone number only after the WMO-designated Regional Specialized
Meteorological Center (RSMC) or Tropical Cyclone Warning Center (TCWC) names a
cyclone. If the RSMC/TCWC has not yet named a cyclone, JTWC uses its TC number,
spelled out, as a placeholder, i.e. "TS 16P (SIXTEEN)."

Q: How are JTWC forecasts different than forecasts issued by tropical
cyclone warning centers (TCWCs) of other countries?

A: JTWC and RSMC/TCWC tropical cyclone warnings may differ for several
reasons. One difference is the measurement of maximum sustained surface winds.
JTWC reports the maximum sustained surface winds in tropical disturbances and
cyclones in terms of 1-minute mean wind speed, as required by the U.S. National
Hurricane Operations Plan. Other nations, however, report maximum sustained
surface winds averaged over a different time interval, which in many cases is
10-minutes. The difference generally means that JTWC will report higher maximum
sustained surface wind speeds than non-U.S tropical cyclone forecasting centers
for the same cyclone. Another difference is that JTWC will issue forecasts out
to 120 hours as required by U.S. DoD. Several TCWCs will transmit forecasts
that extend to a period less than 120 hours. Finally, JTWC does not apply
the same tropical cyclone numbering scheme used by the regional centers. Hence,
the cyclone number assigned by JTWC may not match the numerical designation
assigned to the same cyclone by the responsible RSMC/TCWC.

A: The current (November 2014) JTWC consensus forecast track, CONW, is computed by averaging eight dynamic model and two ensemble mean TC track forecasts. The CONW member tracks are interpolated from the model TC track forecasts as the original (vice interpolated) track forecasts are always produced at or after the forecast time (unavailable to the JTWC Typhoon Duty Officer at forecast production time); thus, an earlier numerical track forecast must be interpolated, then used for CONW computations. The CONW is computed from (listed are the interpolated track forecasts): NVGI, GFNI, AVNI, JGSI, EGRI, ECMI (or, more likely, another available version of the ECMWF forecast such as EMXI or ECM2), COTI, HWFI, and the two interpolated ensemble mean members JENI and AEMI. In order to be considered for the consensus, a model must be consistently available, demonstrate sufficient forecast skill, and add value to the consensus. Models are normally evaluated for one to two years before being included in the consensus. Models that fail to meet these criteria are either not accepted or removed from consensus.

A: When a tropical cyclone closes to within 180 nautical miles of six
designated installations in the western North Pacific, when one of these
installations sets TCCOR 2 or higher, or when directed by USPACOM, JTWC is
required to produce three-hourly updated position graphics on the
"off-hour" tropical cyclone fix cycles (03Z, 09Z, 15Z, 21Z).
The six designated installations are:

Anderson AFB, Guam

Kadena AB, Japan (Okinawa)

Cheju Do, Republic of Korea

Sasebo NS, Japan

MCAS Iwakuni, Japan

Yokosuka NB, Japan

The updated position is derived in a similar manner to the standard best track
position. All available satellite and radar imagery and fixes and synoptic data
are used to determine the most accurate position of the tropical cyclone. A
green triangle labeled "JTUP," which is placed on the graphic
alongside the current forecast track, represents the "off-hour"
estimated position. It is important to note that tropical cyclones move
erratically/wobble in the short term, so there may be some deviation between
the estimated position and the forecast track.